GT isn’t too bad for midges. I’ve never needed spray there.
You will be fine on the red or black depending on whatever length you fancy. The routes can all be done with wheels on the ground and the black is just a little longer and rougher.
If you want a fun but not too taxing day, red in the morning, coffee and cake, then blue in the afternoon? There are only shortish bits of overlap between the two (the first climb) and the blue has lots of fast fun sections and is a great trail.
Folks will no doubt be along shortly to tell you about all of the other options and bits but if you are on your own, it is probably easier just to follow a normal trail and not have to worry about which way you are going all of the time.